The invention relates to lawn mowers and, more particularly, to means for driving a lawn mower cutting blade with the engine crankshaft.
In prior direct drive or clutchless lawn mowers, the cutting blade is driven by the engine crankshaft so that the blade rpm is the same as the engine rpm. Since legislation limits the cutting tip speed of a lawn mower cutting blade, the engine rpm level in these prior lawn mowers is also effectively limited. The maximum allowable cutting tip speed is presently 19,000 ft./min., and this limits the engine rpm, for example, to 3400 rpm for a 21-inch blade.
Because horsepower is a function of rpm, this also limits the power obtainable from an engine with a given displacement.
With prior lawn mowers having the cutting blade directly driven by the engine crankshaft, the possible locations of the cutting blade relative to the engine are limited. For example, engine crankshafts do not pass through the center of the engine, so that a cutting blade mounted on the engine crankshaft cannot be positioned directly below the center of the engine. In other words, if the cutting blade is in the center of the blade housing, the engine cannot be centered on the blade housing.
Also, with these prior lawn mowers, governor response is slowed by reduced engine speeds.
Attention is directed to Heron U.S. Pat. No. 3,402,707, which discloses an engine gearing system.